Dealing with student errors is a central feature of instructional quality. Teachers' reactions to a student's error and classmates' errors can be crucial to the success of a lesson. A teacher should respond appropriately in terms of motivational and learning-related issues so that the error can become a learning opportunity for students. Currently, error situations have rarely been directly recorded and explored in empirical studies. This gap is the central focus of the current study in which we investigated errors in biology instruction within a cross-sectional design where biology lessons in German secondary schools were videotaped, teachers' dealings with errors analyzed, and student achievement documented with pretests and posttests. The study found that constructively dealing with student errors had a significant positive effect on student achievement at the class level. Results confirmed the relevance of teachers' appropriate dealing with student errors on learning in biology instruction.